The subject matter described herein relates generally to a tower base section and a wind turbine and more particularly, to a tower base section of a wind turbine and a system for mounting a tower to a foundation.
Several technical installations require a tower or a mast to transfer reactions from lateral and gravity loads to the supporting foundation. Non-limiting examples of such installations are wind turbines, antenna towers used in broadcasting or mobile telecommunication, pylons used in bridge work, and power poles. Typically, the tower is made of steel and has to be connected to a foundation made of reinforced concrete. The common technical solution is to provide a so-called T-flange with through-holes at the bottom of the tower base section. Anchor bolts are inserted into the through-holes and are fastened in order to connect the base tower section to the foundation.
At least some known wind turbines include a tower and a nacelle mounted on the tower. A rotor is rotatably mounted to the nacelle and is coupled to a generator by a shaft. A plurality of blades extends from the rotor. The blades are oriented such that wind passing over the blades turns the rotor and rotates the shaft, thereby driving the generator to generate electricity.
The lowermost tower section, in the following also referred to as tower base section, of the wind turbine tower is secured to the foundation (e.g., a concrete slab or other suitable foundation). The tower base section may be formed at the lower end as a reverse T-flange with inner and outer through holes for anchor bolts connected to an anchor ring embedded in the foundation. The cross-sectional dimensions of each tower section, and in particular the base section must be sized to withstand all design operational and environmental loads (wind, seismic, ice, snow, etc.) and transfer them to the supporting foundation structure. The magnitudes of the design forces could exceed 2000 kN acting downward and 500 kN/150 kN on the lateral plane at the base of the tower in two orthogonal directions simultaneously. As wind turbine towers have become taller, the cross-sectional dimensions of the tower base section, including the T-flange, have become increasingly larger presenting difficulties in the ground transportation, for example by truck or rail, due to size limitations or roadways, bridges and tunnels through which these sections must pass in route to their assembly destination.
Alternatively, a continuous tower base ring may be used between a tubular lowermost tower section and the foundation. Two rows of anchor bolts, which are circumferentially distributed at a reverse T-flange of the tower base ring, are connected to the anchor ring embedded in the foundation. Higher forces may be transferred safely between the tower and the foundation by increasing the diameter of the tower base ring which leads to the same transportation challenges. The maximum transportable diameter in horizontal position is limited in many countries, for example to 4.3 m in Europe and 4.556 m in the US, due to transportation and logistic restrictions. Accordingly, a vertical transportation of the tower base ring with typical heights of about 1 m is often required. This increases transportation costs.
In view of the above, there is a desire for tower base sections and tower adapters that allow for cost efficient ground transportation and mount of tower base sections with large transverse cross-sectional dimensions.